The correct answer is - 1%.
The grass is a plant, thus it is a producer. It produces food for itself through the process of photosynthesis. The grass though is a food source for the rabbit. From the initial 100% energy from the grass, the rabbit manages to get only 10% of it, thus the rabbit will get just one tenth of the total energy of the grass. The hawk is predator, on the top of the food chain, and the rabbit is its prey. The rabbit only got 10% of the energy from the grass, and the hawk will only 10% of those 10% that the rabbit got. In this way, the hawk will get only about 1% of the initial 100% of energy that the grass had.
